1. Field of the Invention
The present invention relates to a friction stir welding method and a friction stir welding tool for welding a welded member of a metal plate member, an extruded member or the like by friction stirring the welded member.
2. Related Art
There is known a friction stir welding method for bringing a rotating shaft-like tool into contact with a material, softening a welded portion of the material by friction heat, and welding by stirring (refer to, for example, JP-T-07-505090).
JP-T-07-505090 discloses that by moving a probe (distal end portion) of a rotating tool along a butting line while bringing the probe into contact with butted portions of works butted to each other to carry out friction stir, the butted portions are welded.
In addition, there is known a technology of preventing the material from being adhered to the tool by ejecting a cooling agent to the distal end portion of the tool and the welded portion in the above-described friction stir welding (refer to, for example, JP-B2-3530342).
According to the technology of JP-T-07-505090, in the friction stir welding, there is a case in which the tool is thermally expanded in an axial direction by friction heat, the tool penetrates the welded member. In such a situation, not only an excellent welding state is not achieved in the friction stir welding but also there is a concern that the tool is butted to a back up member for backing up the welded member, a die supporting the welded member or the like to destruct the tool.
According to the technology of JP-B2-3530342, although in order to prevent the material from being adhered to the tool by excessive friction heat to retard a welding speed, in order to deprive excessive heat, the cooling agent is ejected to supply to the distal end portion and the welded face, when the cooling agent is applied to the tool distal end portion, there is a concern that the friction heat is not sufficiently generated at the welded portion, the material is softened insufficiently, and an excellent friction stir welding state is not achieved.